The present invention relates generally to signal spectrum analyzers and more particularly, to such analyzers wherein Chirp-Z forward transforms are utilized.
Conventional Chirp-Z signal analyzers utilize forward transforms to compress the individual continuous wave (hereinafter CW) components of the signal into segregated pulses or time intervals from which such components are then selectively reconstructed or expanded with inverse transforms. Considerable gain is inherent with Chirp-Z forward transforms, however, high attenuation is inherent with Chirp-Z inverse transforms. Consequently, Chirp-Z inverse transforms incumber the overall sensitivity of signal analyzers.
To avoid the high attenuation associated with Chirp-Z inverse transforms, selected CW components can be reconstructed from the Chirp-Z pulses relating thereto, by replicating each of those pulses for the time period separating therebetween. A disclosure regarding this technique entitled SAW Tapped Delay Lines For New Potential Circuit Applications, was published by William J. Skudera, Jr. in the Proceedings Of The 42ND Annual Symposium On Frequency Control 1988. In this disclosure, the replications of each pulse are separated by half the uniform Chirp-Z pulse duration and are derived with a tapped delay line (hereinafter TDL) that generates an initial group of replications which is enhanced in number by continual recirculation therethrough until the following Chirp-Z pulse appears. Such recirculation is accomplished through a feedback switch which functions to initiate the reconstruction process for each successive pulse. With each circulation however the number of pulse replications emitted from each tap of the TDL expands, so that some pulse replications stack upon others which causes increasing distortion and possible instability, as the number of recirculations increases.